This research is aimed at determining the mechanisms whereby the asymmetical morphologic pattern is established along the anteroposterior and proximodistal axes. The role of a morphogenetic factor in the establishment of anteroposterior polarity is being investigated. The factor is found in both low molecular weight and high molecular weight forms. We are investigating possible models of this with reference to current hypothetical models for polarity control. One of these is a diffusion gradient model; another involves close range cell-cell interactions. The role of the ectodermal ridge in the proximodistal development of limb is being examined. Using myogenesis in vitro as an indicator of a state of "determination", evidence suggests the ridge may keep underlying cells in a relatively undetermined state. Transplantation studies indicate that only this tissue is capable of responding to more proximal signals regarding the proximodistal level developing.